Find the word definition

Wiktionary
party dress

n. A woman's dress that is too elegant, revealing, dressy or impractical for normal wear.

Wikipedia
Party dress

A party dress is a dress worn especially for a party. Different types of party such as children's party, cocktail party, garden party and costume party would tend to require different styles of dress. One classic style of party dress for women in modern society is the little black dress.